1. Field of the Invention
The present invention relates to an illumination apparatus and an illumination method, and more particularly, to an illumination apparatus and an illumination method performing illumination with diffraction beam.
2. Description of Related Art
An illumination apparatus employing a laser source is typically used in an optical apparatus such as an inspection apparatus, a projector, or an exposure apparatus. The laser source is typically a point light source, which makes it difficult to perform uniform surface illumination (area illumination). However, it is preferable to perform surface illumination in uniform light intensity distribution when an object is illuminated. Therefore, an optical system called uniformizing optical system is sometimes used as the light source used in the inspection apparatus or the exposure apparatus or the like. More specifically, the optical system called fly-eye lens or kaleidoscope is widely used as the uniformizing optical system. The uniformizing optical system is described in “Optical Technique Contact”, Vol. 33, No. 2, pp. 41-44 (1995), for example. The optical apparatus uniformizing the beam with a plurality of optical fibers is also disclosed in Japanese Unexamined Patent Application Publication No. 2005-308967.
However, a micro fly-eye lens is needed in the optical system with narrow field. In the conventional technique, it is difficult to form such a micro fly-eye lens with high accuracy. Further, coherence length of the laser beam increases because the laser beam has narrow spectrum width. Therefore, when the laser source is used as the light source for illumination, speckle (patchy pattern of dark spots and bright spots) is generated due to the temporal coherence of the laser beam, which causes noise on the image. Therefore, in the conventional illumination apparatus, it is difficult to decrease the speckle noise by the uniform illumination.
An object of the present invention is to provide an illumination apparatus and an illumination method that can decrease the speckle noise and achieve uniform illumination.